Process for controlling the cooling process in a tunnel furnace



Aug. 2, 1966 P. scHWAMBoRN ET AL 3,263,738

PROCESS FOR CONTROLLING THE COOLING PROCESS IN A TUNNEL FURNACE Filed Aug. 17, 1964 5 Sheets-Sheet 1 INVENrOIPS Aug. 2, 1966 SCHWAMBQRN ET AL 3,263,738

PROCESS FOR CONTROLLING THE COOLING PROCESS IN A TUNNEL FURNACE Filed Aug. 17, 1964 5 Sheets-Sheet 2 Aug. 2, 1966 P. SCHWAMBORN ET AL 3,263,738

PROCESS FOR CONTROLLING THE COOLING PROCESS IN A TUNNEL FURNACE Filed Aug. 1'7, 1964 5 Sheets-Sheet 5 lM LfA/fOPS United States Patent 1 Claims. (01. 165-2) This invention relates to the control of the cooling process in a tunnel furnace which may be either of the kind working with continuous advance of the cars or of the kind operating in the conventional and still frequently practised manner with intermittent advance of the cars.

The calibration of a cooling curve adapted to the special characteristics of the material to be treated is one of the main conditions for the perfect functioning.

of all tunnel furnaces. The curve must be set up in principle for any given material. Its maintenance, however, requires frequent control operations because the furnace output is variable. Both the feed velocity and the charge density on the cars may be subject to considerable variation which must be constantly compensated.

The difficulties in producing optimum cooling conditions from case to case are particularly based on the differential sensitivity of the treated material to the cooling action which is exceptionally high in certain temperature intervals, in particular in the region of the quartz transformation point of about 575 C., and in the temperature range between 180 to 200 C., and is relatively small in other intervals, i.e., that between the sharp calcining temperature and the first quartz transformation point.

Normally, direct cooling of the material is therefore out of the question. Preference is given to indirect cooling, for which many methods are known which fulfil the purpose in a more or less satisfactory manner. Ptarticul-arly advantageous has been found a cooling system developed in the last two years by means of dampers supplied with a gaseous or liquid cooling medium arranged directly in the furnace channel below the vault and/or in front of the side walls thereof. Such cooling dampers have the advantage of exceptionally intensive cooling action and in addition provide facilities for regulating the cooling action as required by controllable blanking of the cooling units by means of dampers.

Difiiculties arise, however, in particular in the region directly adjoining the calcining zone in which, for example when treating sintered material or refractories, temperatures may rise considerably above i000 C.

These high temperatures make exacting demands both on the temperature resistance and on the resistance to sudden changes in temperature in particular of the covering dampers, which are subject to relatively rapid wear. Moreover, the arrangement of the dampers on constructional member-s which support them or guide them is such that there must be spaces between the individual cooling units to accommodate the dampers which vary the coverage of the unit. These spaces result in undesirable kinks in the cooling curve.

Moreover the dampers do not permit complete local elimination of the cooling action of the units as may be desirable, for example in the range of the dangerous temperature intervals mentioned above under fluctuating furnace output.

It is impossible to do this by switching off sections of the cooling unit themselves because in this case the units would rapidly be destroyed under the action of the high temperature.

3,263,738 Patented August 2, 1966 The present invention relates to tunnel furnaces cooled by units arranged in the furnace channel through which a cooling medium flows, and permits both the avoidance of these difficulties and disadvantages and simplification of the total construction of the cooling zone and, moreover, further improvement in the fine adjustment and uniformity of the cooling curve.

In accordance witlrthe basic principle of the invention this is achieved by dispensing with covering valves, dividing the cooling system into a large number of cooling units, i.e., pipelines through which cooling medium flows or sections of pipelines, designing these to be separately movable, i.e., .shiftable in the longitudinal direction of the furnace channel, or with-drawa-ble therefrom, and effecting control of the cooling curve by longitudinal movement and/ or removal of such units.

This permits the most advantageous adjustment of distances between successive units to be obtained. Further, when successive units are arranged staggered relative to the longitudinal axis of the furnace in accordance with a special characteristic of the invention, it is possible to place the units either in a fully exposed or in an overlapping position, i.e., to create an interrupted inner wall of the furnace channel supplied with effective cool-ing units, and to create, for example, regions in which, by contrast with what has previously been possible, the cooling action is locally reduced to zero according to plan.

The overlapping of two units in this manner considerably reduces the proportion of cooling by radiation and that by convection, down to the cooling action of only one unit, so that the uncooled region is not by any means followed by an exceptionally violently cooled region.

A further possibility for fine control of the cooling process is obtained in that, with appropriate design of the units as coiled tubes, the windings of the overlapping units are not flush but are arranged with a lateral distance between them. Overlapping of the units then produces intensive local cooling. Units of this design can extend over the entire length of the part of the cooling zone fitted with units, but can if necessary be restricted to sections of this region, i.e., those sections in which control processes must be effected with exceptional frequency.

The above examples show the many possibilities for the adjustment of the cooling curve which are provided by the method according to the invention without provision having to be made for screening devices for the units with the disadvantages which the use of such devices involves, as described above.

The independently shiftable or movable units may be connected in parallel or in series by flexible tubes with a common cooling medium pipeline, or with one another.

Suitable cooling media are gaseous media such as air but preferably, because of the more intensive cooling action, liquid media such as water are used, as in the known cooling systems using cooling units. The use of oil as the cooling medium is particularly advantageous, because the difiiculties .are then avoided which arise when water is used because of the pressure which builds up in the pipelines. When water is used as the cooling medium, considerable pressure builds up in the pipelines at the temperatures involved (about 250 0), whereas when oil is used no liquid pressure builds up at such temperatures.

In accordance with a special embodiment of the method of the invention the facilities provided, for controlling the cooling process in a tunnel furnace, are further perfected in that the cooling units which can be shifted in the longitudinal direction of the furnace channel are combined with fixed structures in the furnace channel which are so designed and arranged that the shiftable cooling units can as desired be placed more or less completely behind these structures in order to screen them to the extent desired from the interior of the furnace channel.

This further improves the facilities for obtaining uniform temperature distribution across the furnace channel cross-section because, for example, with partial covering of the units by the fixed screens behind which the cooling units more or less completely disappear, the remainder thereof can extend without interruption over the entire circumference of the furnace channel and thus exert a corresponding cooling action on the entire cross-section of the furnace channel. The width of the units and of the fixed screens can be varied within wide limits, so that advantageous facilities of adaptation are provided in this respect also. The problem of the movable design of the cooling units can also be simplified by the arrangement of the screens and their movement can if desired be controlled automatic-ally without diificulty as a function of temperature.

According to a further characteristic of the invention, the fixed screens can be so designed that their screening action is more or less intensive, for example, the successive screens in the longitudinal direction of the cooling zone can consist of material of diiferent heat conductive properties, of greater or lesser wall thickness or can be provided with perforations in order to adapt the screening action to the particular temperature conditions in the appropriate region of the furnace channel.

A special advantage of the cooling zone of a tunnel furnace according to the invention which comprises intermittently advance'able cars carrying the furnace charge is that the cooling units situated behind the fixed screens may be moved from behind the screens rapidly only when the advance of one car has taken place, so that they exert their cooling action uniformly on the entire length of the car or of the charge on it, to be retracted behind the screens before the cars next advance. This uniform cooling action on the charge of a car which is arrested for some time is particularly important when the car contains elongated material, e.g., plates of appropriate length.

The fixed screens behind which the cooling units may be moved as desired need not be associated with each of the many cooling units distributed along the length of the cooling zone. As a rule it is sufficient to make provision for them only in the regions of the furnace channel where the temperatures are highest, i.e., directly after the calcining zone, and in the regions where it is important that the cooling action should be controllable, e.g., the temperature range of quartz transformation. It is, of course, unnecessary to associate all the cooling units with fixed screens.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which FIGURE 1 shows an axial vertical section through a part of a tunnel furnace;

FIGURE 2 is a horizontal section corresponding to FIGURE 1;

FIGURE 3 is a cross-section along the line IIIIII of FIGURE 2;

FIGURE 4 is a view similar to FIGURE 1 showing the arrangement of the fixed screens for the movable cooling units in the furnace channel; and

FIGURE 5 is a vertical section through the furnace channel along the line VV of FIGURE 4.

In the drawings, the cooling units are represented as rectangles and two cooling units succeeding one another in the longitudinal direction of the furnace channel are marked and d. The units c, d are connected to a cooling medium feed pipe (not shown) by flexible pipelines f, 7 which pass through covered slots e, e" in the furnace channel walls (FIGURE The dimensions of the slots e, e are preferably such that the cooling units can be removed as a whole through the slots.

The means for moving the cooling units in the longitudinal direction of the furnace channel are not shown. It is advisable to suspend them for this purpose from trolleys on carrier devices extending through slots in the furnace channel wall or in the vault. The arrangement obtained if the cooling units are arranged in the horizontal position in the vault of the furnace channel is fundamentally the same as that shown, except that the position is turned through FIGURES 1 and 2 show that the cooling units which can be moved in the longitudinal direction of the furnace channel whose walls are designated a and through which the train of cars advances in the direction of the arrow, extend without interruption along the entire length of the part of the furnace channel equipped with the cooling units. FIGURE 2 further shows the preferred staggered arrangement of the cooling units relative to the longitudinal axis of the furance channel. This arrangement permits successive units to cover one another entirely or partly for the purpose explained above and thus both to influence the cooling action in the region in which the cooling units overlap and to create, as desired, a non-cooling zone which is not cooled by the cooling unit 0 or d which is pushed in front of the neighbouring unit. Such non-cooling zones can be of advantage in particular in those regions in which the material is exceptionally sensitive to cooling. These noncooling zones can extend along the length of a cooling unit or, when, according to FIGURE 2, one of the inner units d has been moved rearwandly in front of an adjacent outer unit 0, can be given double the length by moving the following outer unit forwardly behind the following inner unit.

The distance through which the cooling units can be moved may be limited but, by contrast with the embodiment shown, the layout can be so arranged that the units can be moved to any points of the length of the furnace channel by means of the moving device (not shown) from which they are suspended or on which they rest.

Figure 4 is a view which corresponds approximately to the end of the calcining zone. In FIGURE 4 the letters b, b" indicate fixed screens provided according to the embodiment illustrated, behind which the cooling units c, c" can be moved from their active positions (shown in solid lines) to their fully screened position (shown in dotted lines).

In accordance with FIGURE 5, the screens b, b" which have a thinner wall thickness than in FIGURE 4 extend as far as the vault of the furnace channel so that open chambers are only formed at their ends into which the cooling unit 0', 0 can be moved as desired to a greater or lesser extent.

The invention is not restricted to the embodiments described in detail and illustrated in the drawings, but changes in many respects can be effected without deviating from the invention as defined in the ensuing claims. It is of course possible within the scope of the invention to effect the screening of cooling units, in particular in the regions of the cooling zone in which lower temperatures predominate, in some other way, for example em ploying movable slides.

What is claimed:

1. A process for controlling the cooling process in a tunnel furnace having a furnace channel defined by side walls, which channel is cooled indirectly by a plurality of laterally spaced rows of mutually independent cooling units arranged respectively close to said side walls, through which cooling units a fiuid cooling medium flows, comprising moving selected units of one row independently of the other row in the longitudinal direction of the furnace channel behind screen means for the purpose of controlling the cooling process.

2. The process claimed in claim 1, in which the cooling effect of the cooling units is controlled by moving the cooling units behind fixed screens which screen them against the interior of the furnace channel over an area of their effective surface which can be selected as desired.

3. The process claimed in claim 1 when employed in a furnace in which a furnace charge advances intermittently along the furnace channel, in which, immediately prior to an advance of the charge, the cooling units are placed behind said screen means, and, after each advance, are immediately withdrawn from behind said screen means, and ane therefiore brought to exert their influence practically simultaneously on the entire length of the charge. I

4. In a tunnel furnace comprising a furnace channel defined by side walls, and a plurality of cooling units arranged within the channel close to the side Walls, means for moving said cooling units independently in the longitudinal direction of the furnace channel, said cooling units in the longitudinal direction of the furnace channel staggered relative to the furnace axis in a manner such that the successive unit can be arranged to overlap each other to any desired extent to expose an area of the furnace walls.

References Cited by the Examiner UNITED STATES PATENTS 9/1961 Knight 263- X 9/ 1963 Cremer et a1. 263-28 ROBERT A. OLEARY, Primary Examiner. FREDERICK L. MATTESON, JR., Examiner.

M. A. ANTONAKAS, Assistant Examiner. 

1. A PROCESS FOR CONTROLLING THE COOLING PROCESS IN A TUNNEL FURNACE HAVING A FURANCE CHANNEL DEFINED BY SIDE WALLS, WHICH CHANNEL IS COOLED INDIRECTLY BY A PLURALITY OF LATERALLY SPACED ROWS OF MUTUALLY INDEPENDENT COOLING UNITS ARRANGED RESPECTIVELY CLOSE TO SAID SIDE WALLS, THROUGH WHICH COOLING UNITS A FLUID COOLING MEDIUM FLOWS, COMPRISING MOVING SELECTED UNITS OF ONE ROW INDEPENDENTLY OF THE OTHER ROW IN THE LONGITUDINAL DIRECTION OF THE FURNACE CHANNEL BEHIND SCREEN MEANS FOR THE PURPOSE OF CONTROLLING THE COOLING PROCESS. 